75 lines
2.7 KiB
Java
75 lines
2.7 KiB
Java
public class QuadraticRoots {
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private static class Complex {
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double re, im;
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public Complex(double re, double im) {
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this.re = re;
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this.im = im;
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}
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@Override
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public boolean equals(Object obj) {
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if (obj == this) {return true;}
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if (!(obj instanceof Complex)) {return false;}
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Complex other = (Complex) obj;
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return (re == other.re) && (im == other.im);
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}
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@Override
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public String toString() {
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if (im == 0.0) {return String.format("%g", re);}
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if (re == 0.0) {return String.format("%gi", im);}
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return String.format("%g %c %gi", re,
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(im < 0.0 ? '-' : '+'), Math.abs(im));
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}
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}
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private static Complex[] quadraticRoots(double a, double b, double c) {
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Complex[] roots = new Complex[2];
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double d = b * b - 4.0 * a * c; // discriminant
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double aa = a + a;
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if (d < 0.0) {
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double re = -b / aa;
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double im = Math.sqrt(-d) / aa;
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roots[0] = new Complex(re, im);
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roots[1] = new Complex(re, -im);
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} else if (b < 0.0) {
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// Avoid calculating -b - Math.sqrt(d), to avoid any
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// subtractive cancellation when it is near zero.
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double re = (-b + Math.sqrt(d)) / aa;
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roots[0] = new Complex(re, 0.0);
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roots[1] = new Complex(c / (a * re), 0.0);
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} else {
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// Avoid calculating -b + Math.sqrt(d).
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double re = (-b - Math.sqrt(d)) / aa;
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roots[1] = new Complex(re, 0.0);
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roots[0] = new Complex(c / (a * re), 0.0);
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}
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return roots;
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}
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public static void main(String[] args) {
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double[][] equations = {
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{1.0, 22.0, -1323.0}, // two distinct real roots
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{6.0, -23.0, 20.0}, // with a != 1.0
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{1.0, -1.0e9, 1.0}, // with one root near zero
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{1.0, 2.0, 1.0}, // one real root (double root)
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{1.0, 0.0, 1.0}, // two imaginary roots
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{1.0, 1.0, 1.0} // two complex roots
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};
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for (int i = 0; i < equations.length; i++) {
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Complex[] roots = quadraticRoots(
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equations[i][0], equations[i][1], equations[i][2]);
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System.out.format("%na = %g b = %g c = %g%n",
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equations[i][0], equations[i][1], equations[i][2]);
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if (roots[0].equals(roots[1])) {
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System.out.format("X1,2 = %s%n", roots[0]);
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} else {
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System.out.format("X1 = %s%n", roots[0]);
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System.out.format("X2 = %s%n", roots[1]);
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}
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}
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}
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}
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